1. Field of the Present Invention
The present invention relates to a method for forming π-type bus electrode, and more particularly, to a method for improving the adhesion capability between the π-type bus electrode and indium tin oxide (ITO) electrode.
2. Description of the Related Art
Indium is a kind of rare metal. It is similar to silver, yet the quantity of which in the crust is about 5-10%, only 1% of that of silver. In nature, indium exists in mixture with other mineral substances in very small quantity. Now about fifty kinds of mineral substances are discovered to contain indium, in which lead zinc minerals that contain sulfur has the largest quantity of indium while tinstone, wolframite, and ordinary uralite also contain a larger quantity of indium. Besides, some dust produced by thermal power plants also contains indium. At present the mineral substance that is worth industry recycling is mainly sphalerite. In general, sphalerite contains about 0.001% to 0.1% of indium.
Indium is a metal that is silver white and a little light blue, softer than lead in its hardness, the melting point of which is about 156.6° C. and the density of which is about 7.3 g/cm3. It has good expandability, conductivity, and plasticity, and is able to be pressed into an extremely thin slice. Indium has chemical properties similar to those of iron, slowly reacting to oxygen in the air between normal atmospheric temperature and its melting point and forming very thin oxide film on its surface. Indium has very good anti-corrosiveness to seawater and reflectivity to light, being able to reflect almost all the colors on the spectrum. Besides, indium can form alloy with many other kinds of metal such as Ag—Pb—In alloy that can be material of bearing of high-speed aero-engine and Indium-Tin alloy that can be vacuum airtight material, material for contact of alloy of low-melting point, or binding material between glass and glass or glass and metal.
So far in the industry, the largest market of application of indium is function material. In general, indium is used in the form of indium tin oxide as transparent electrode that serves as display panel, which is widely applied in thin film transistor, liquid crystal display panel or plasma display panel.
Referring FIG. 1A, a top view of a layer of indium tin oxide transparent conductive film 102 is formed on a glass substrate 100, in which the portion of slashes is a glass substrate 100 and the other portion is an ITO transparent conductive film 120. The ITO (indium tin oxide) transparent conductive film 120 is formed on glass substrate 100 by methods such as Thermal Evaporation Deposition, sputtering, Electron Beam Evaporation, Spray Pyrolysis, Chemical Vapor Deposition, or Pulsed Laser Deposition. In these methods, sputtering process has merits such as being able to form film of large square measure, film of even thickness, and reproducible thin film and is a process that is widely used at present. And through adjusting the parameters of film that forming in sputtering process such as distance between target material and glass substrate 100, thickness of thin film, and conditions of sputtering, the properties of ITO transparent conductive film 120 can be precisely controlled.
Then, conductive layer as bus electrode such as silver paste is formed on ITO electrode 102 and glass substrate 100 by print method. A π-type (or referred to pi-type) bus electrode 104 is then formed by lithography method, the pi side 106 of the pi-type bus electrode 104 being on ITO electrode 102 and portion of stripes 108 of the pi-type bus electrode 104 being on glass substrate 100, as shown in FIG. 1B.
Since pi-type bus electrode 104 is composed of silver and small sum of glass powder, there is good adhesion capability between portion of stripes 108 of the pi-type bus electrode 104 and glass substrate 100, but worse adhesion capability between the pi side 106 of the pi-type bus electrode 104 and ITO electrode 102. Therefore, the edge warp phenomenon of the pi side 106 of pi-type bus electrode 104 will occur, as shown in FIG. 10. And the edge warp phenomenon for the pi side 106 of pi-type bus electrode 104 will cause the point discharge effect of pi-type bus electrode, which hinders the following process to proceed.
In conventional art, a layer of edge warp preventer, which is not shown in the figure, is formed on pi-type bus electrode 104 before put under the firing process to prevent the edge warp phenomenon 110 of pi side 106 of pi-type bus electrode 104 occurred when ITO electrode 102 and pi-type bus electrode 104 are under the firing process. Although a preventer can be used to prevent the pi-type bus electrode from the edge warp phenomenon, yet the cost is getting higher and the process has complicated steps, which are the disadvantages of conventional solution.